In conventional optical lithographic practice a thin film of a photoresist material is applied to a substrate. The photoresist film is exposed to a desired pattern of radiation and the exposed photoresist is developed to reproduce the desired pattern. The pattern can be reproduced onto the surface of the substrate by an etching process. However, in this approach resolution is limited by the wavelength of the exposure radiation and as the feature size becomes smaller the equipment becomes increasingly expensive and complex.
Imprint lithography (IL) has gained considerable attention as a cost effective and technically feasible method for fabricating nanometer-dimension structures. Due to its low cost relative to conventional optical lithography tools and next generation lithographies (NGL), and because of the apparent ability to produce devices with critical dimensions as small as 10 nm, IL can play an important role in the integrated circuit and hard disk drive industries as well as telecommunications, specifically in the production of surface acoustic wave devices.
For imprint lithography techniques generally, a relief pattern in a template is used, in conjunction with polymeric materials to create a desired pattern on a substrate. The process, illustrated generally in FIGS. 1a–1d, involves coating the surface of a substrate 110, that can be silicon or quartz, with a thin film of a deformable polymer material 115 (FIG. 1a). Subsequently, the film is imprinted with a pattern of trenches by applying pressure to a patterned template 120 (FIG. 1b). Application of pressure can be mechanical or by fluid pressure such as disclosed in U.S. Pat. No. 6,482,742 to Chou. The imprinted film can be cured by the application of heat, illumination, pressure or combinations thereof. Following the curing step (FIG. 1c), a reactive ion etch (RIE) process can be used to remove unwanted material from the trenches imprinted on the surface of the polymer film and transfer the pattern into an under lying structure that can be the substrate or other functional thin films (FIG. 1d) (cf. Voisin, U.S. Patent Application Publication US 2003/0205657, Nov. 6, 2003). The imprint lithography process is discussed in detail in U.S. Pat. No. 5,772,905 to Chou.
For integrated circuit manufacturing or other high resolution applications, the template should have a precise pattern that pressing transfers, inherently with minimal demagnification, to the surface of the integrated circuit device.
Numerous variations of the basic IL method outlined above have been developed. Discussions of these methods can be found in Bailey et al., J. Vac. Sci. Tech. B 18(6), 3572–3577 (2000), Colburn et al., Proc. SPIE, 3676, 379–389 (1999), Tan et al., J. Vac. Sci. Tech., B16(6), 3926–3928, (1998), and Sreenivasan et al., Proc SPIE, 4688, 903–909 (2002).
One particular IL component critical to its cost effectiveness is the template or mask. According to a cost-of-ownership study by Sreenivisan (ibid.), the IL mask is estimated to cost about $40,000. This mask cost assumes volume production and an inspection and repair infrastructure that is not currently available. Actual mask cost in prototyping volumes will likely approach $100,000, particularly since the mask is a “1×” technology. That is, the feature sizes that are printed are equal to their corresponding features on the mask. This is in contrast to the reduction technology practiced in most commercial optical photolithography technologies that typically employ 4× or 5× reduction. As with all masks, as the feature size of IL masks decreases, the time required to pattern or “write” a mask increases. Consequently, not only does the mask cost increase but also the turnaround time to fabricate a mask increases. Thus, for small-volume manufacturing and prototyping, mask costs can become prohibitively expensive, i.e., the mask amortization cost schedule far exceeds the technology generation duration.